NDP candidate Joe Cressy has spent the week pillorying his Liberal rival, former city councillor Adam Vaughan, for skipping a debate on climate change. He maintains Vaughan absented himself rather than defend Liberal Leader Justin Trudeau’s support for the proposed Keystone XL pipeline, which would carry bitumen from Alberta to refineries on the U.S. Gulf coast.

“If Justin Trudeau and Adam Vaughan want to be the Keystone candidates, they have to defend it. It’s not enough to ignore the voters,” Cressy said in an interview, adding that he’s never once heard Vaughan, an environmental activist in his own right, defend Keystone.

The oil sands are the single biggest source of greenhouse gas emissions, which contribute to climate change, in Canada. And that, said Cressy, is of concern to voters in Trinity-Spadina.

“Climate change, it’s one of the defining issues of our time,” he said.

“People in downtown Toronto talk about it a lot … Climate change is now real here in downtown Toronto. We had this ice storm last winter, we had flooding last summer, we had a heat wave like we’ve never had just a year ago.”

But the oil sands are also one of the biggest sources of economic growth in the country.

Consequently, the Conservatives are enthusiastic advocates of pipelines to fulfil Prime Minister Stephen Harper’s dream of turning Canada into an energy superpower. The Harper government has been pushing Keystone and this week approved the Northern Gateway pipeline from Alberta to British Columbia’s environmentally sensitive northern coast, subject to 209 conditions.

Trudeau is opposed to Northern Gateway. But he’s open to another proposed pipeline to B.C.’s coast, Kinder-Morgan, which he considers less environmentally risky. And he’s a staunch supporter of Keystone, which has been approved by Canada but is stalled in the U.S.

My pipeline is better than your pipeline kind of conversations frankly don’t change the yardsticks on the climate change dynamic

NDP Leader Tom Mulcair is opposed to all three. He favours a west-east pipeline that would carry the bitumen to refineries in Atlantic Canada.

Vaughan denies he skipped the climate change debate to avoid talking about Keystone. In an interview, he said there was some confusion about the timing and, in the end, he couldn’t make it because he had other commitments.

Vaughan insisted he’s not afraid to defend Keystone but finds pipeline politics unproductive. He noted that none of the three main parties advocates shutting down the oil sands and each has their preferred pipeline for getting the bitumen to market.

Vaughan doesn’t disagree with Cressy that climate change is a defining issue. But for him, “wedge politics” over pipelines is not the crux of the matter; the real issue how to make cities, which he called the biggest engine of greenhouse gases in the country, more energy efficient.

“At the end of the day, if cities don’t stop burning and wasting fossil fuels, we’re going to be sucking oil out of every corner of the planet to feed a beast that, quite frankly, can be tamed,” he said, citing better housing, public transit and infrastructure as the solution.

The NDP has held Trinity-Spadina since 2006, when Olivia Chow took the seat from the Liberals. Chow, the widow of late federal NDP leader Jack Layton, resigned to run for mayor in Toronto’s municipal election this fall.

The byelection, scheduled for June 30, is seen as a crucial battle in the NDP-Liberal war over which opposition party is the real government-in-waiting.

Trudeau and NDP Leader Tom Mulcair have been in the riding multiple times since the byelection was called last month. Mulcair is to campaign with Cressy again today.

Earlier this week, Mulcair waded into the pipeline fray.

“I think that there are people in places like Trinity-Spadina that realize that Joe Cressy is the right person for the job because he’s part of a team that understands that there’s no sustainable development if you’re shipping raw bitumen and shipping your jobs out of the country,” Mulcair said.

“So people know that we’re the only ones standing up on these issues against Keystone XL and that’s a defining difference between the NDP and the Liberals.”

She talks the talk and she walks the walk on these tough issues of sustainable development and she gets elected time after time

He maintained the party’s stance won’t hurt its already slim chances in Macleod and Fort McMurray-Athabasca, the two Alberta ridings also facing June 30 byelections. The Conservatives are expected to easily hold onto both.

“These are not ridings that have been naturally devolved to the NDP, as you know. But these are issues that are important to everyone,” Mulcair said.

He noted that the NDP’s sole representative in Alberta, Edmonton MP Linda Duncan, is an environmental lawyer.

“She talks the talk and she walks the walk on these tough issues of sustainable development and she gets elected time after time. And that reassures me that a lot of people in Alberta understand the importance of sustainable development.”

A second Toronto riding, Scarborough-Agincourt, will also choose a new MP on June 30.